A spring-driven nail gun that retracts a plunger against a resilient force of a spring and then releases the plunger for impacting a nail to a workpiece have been wellknown as an electric power tool. U.S. Pat. No. 3,589,588 discloses an electric power tool having a plunger which is retracted by a mechanism including a motor and decelerating gears in the tool, which reduces power required to retract the plunger. The tool includes a detecting switch that detects a release operation of the plunger. When the release operation is detected, the tool stops feed to the motor.
In the above tool, even when the detecting switch is breakdown, the tool is able to perform a normal operation to impact the nail. When this case happens, a user may miss this failure and keep using the tool, because the tool is able to impact the nail. This condition may lead to a risk that the motor may keep rotating after the impacting operation is over, and cause unintentional continuous impacting operations.
An object of the invention is to provide a fastener driving tool which ceases an impacting operation in case a detecting switch is breakdown.